Chronic active hepatitis C is a major health concern in the United States and worldwide. Hepatitis C virus (HCV) is primarily transmitted through contact with infected blood, with known risk factors including injection drug use, receipt of blood or blood products prior to 1992, tattoo and body piercing, and nosocomial exposure. Although much is known about HCV transmission, a substantial proportion of infected individuals report no identifiable source of exposure. Unexplained cases of HCV are particularly high among noninjection drug users, indicating a potential hidden source of infection within this group. One hypothesis to account for these unexplained cases is that HCV may be transmitted through contaminated sniffing/snorting implements, such as straws or spoons, shared by intranasal drug users. Snorted cocaine and other powdered drugs can irritate the nasal membranes causing deterioration, leakage and bleeding. When inserted into the nasal cavity, a sniffing implement may come into contact with HCV-infected nasal secretions or blood, which may then be transmitted to an uninfected individual sharing the same implement. Although several studies have shown intranasal drug use to be a significant risk factor for HCV infection, there is nearly a complete absence of virological, clinical, and behavioral data pertaining to this potential mode of HCV transmission. The proposed pilot study will help fill these research gaps by achieving the following specific aims: (i) develop reliable methods and perform laboratory assays to detect HCV RNA in the nasal secretions of plasma-positive intranasal drug users and on the surfaces of drug-sniffing implements; (ii) develop methods and perform assays to test for the presence of blood in nasal secretions and sniffing-implements, (iii) develop measures, collect preliminary data, and evaluate the psychometric properties of an instrument to assess risk factors that may be associate with intranasal HCV transmission; and (iv) develop and evaluate protocols for clinical examination and assessment of nasal cavity pathology among chronic drug-sniffers. While these aims focus on the development of new technologies and the collection of preliminary data for future research, the proposed study will, nonetheless, resolve several fundamental questions regarding the preconditions necessary for intranasal HCV transmission.